1. Field of the Invention
The present invention relates to a data storage device for recording data used in information equipment.
2. Description of the Related Art
With the recent development and spread of information equipment, there has been a rapid increase in the amount of data to be stored in a storage device in the equipment. In general, storage devices are subject to a limitation on their storage capacity. When the storage capacity is exhausted, users have to add a new storage device or medium or delete data already stored. To cope with the limited storage capacity, conventional supervisory camera systems adopt a method which involves automatically deleting old image data and then writing new image data.
FIG. 1 illustrates a method to delete files in conventional information equipment. The information equipment 11 is composed of a CPU (Central Processing Unit) 12, a memory 13, an input/output device 14, and a storage device 15, which are all interconnected by a bus 16. When a new file 17 is added to the storage device 15, an old file is deleted automatically and the file 17 is then written into the vacated memory area.
However, with information equipment, such as a personal computer (PC), old data is not always garbage. Deleting a file in the same way as above may result in loss of important data. Therefore, the demand has increased for reserving free storage space automatically taking into account the significance of data.